Conventional imaging methods used for a medical imaging diagnosis roughly include radiography for obtaining still images and fluoroscopy for obtaining moving images. Appropriate imaging apparatuses are selected for these imaging methods as needed.
Radiography generally uses a screen film system that combines a fluorescent screen and a film. This method includes a method for exposing and developing a film and then fixing it and a method for recording radiation images on a photostimulable phosphor as latent images and then scanning with laser to read out the images.
However, the above-described methods does not yield instant results because of a complex workflow to obtain radiation images.
Fluoroscopy generally uses an image intensifier. However, since this method uses an electron tube, the apparatus is bulky, the visual field region is restricted, and distortion and crosstalk are significant.
Under the circumstances, radiation imaging apparatuses capable of instantaneously obtaining a high-quality image with a large area, and various proposals are expected.
Japanese Patent Application Laid-Open Nos. 08-116044 and 2003-218339 disclose radiation imaging apparatuses using a sensor array formed by two-dimensionally arrayed pixels each including an MIS sensor and a TFT. The radiation imaging apparatus disclosed in Japanese Patent Application Laid-Open No. 08-116044 alternately executes a photoelectric conversion operation and a refresh operation continuously in the whole sensor array. The radiation imaging apparatus disclosed in Japanese Patent Application Laid-Open No. 2003-218339 executes the refresh operation not in the whole sensor array but for each vertical scanning line.
However, these conventional radiation imaging apparatuses have an operation period for the refresh operation independently of an operation period for photoelectric conversion. It is therefore difficult to continuously execute photoelectric conversion at a high speed.
The refresh operation requires a time of about 10 ms to several ten ms per frame in some cases in consideration of the potential variation of the sensor array. This time is non-negligible relative to 30 FPS (30 frames per sec), i.e., 33 ms/frame necessary for fluoroscopy. This makes it difficult to realize fluoroscopy.